EDIT: Sorry I just re-read your question… Yes you can run docker on FreeNAS but there is NOT a “docker tab” I think you have would have to configure docker manually.
The short answer I think is yes. I’ve only played with docker a few years ago when it first released. Now getting Hass.io running, for example, might not be so straightforward. I’m sorry I don’t have the knowledge to better speak about this. For my current use case docker is just to much overhead. And there is overlap between what FreeNAS already provides and the add-ons provided with Hass.io. For example Samba and ssh are already available and easily configured through the native FreeNAS GUI. I have only briefly looked at trying to get Hass.io running on FreeNAS but at this time it’s just been much easier to get the components (like AppDaemon, Node Red, Mosquitto…) running by themselves. For me it’s just easier to make a new Jail. I have been slowly working on some other scripts make installing these other “add-ons” easier but work is getting in the way